The realm of low-expansion cordierite bodies (CTE&lt;10.times.10.sup.-7.degree./C.) has previously been limited to ceramics prepared by firing mixtures of crystalline raw materials (e.g., clay+talc+alumina) at temperatures above 1375.degree. C. These low expansions rely largely upon microcracking, which is induced by the anisotropic thermal expansion/contraction of cordierite crystals or crystal aggregates that form as a consequence of the manner by which cordierite nucleates and grows from the reactive raw materials.
In extruded honeycomb bodies in which platelet-shaped particles of the raw materials tend to orient with their longest dimensions in the direction of extrusion, it is commonly observed that the cordierite crystals grow with their negative-expansion c-axes lying in the plane of the walls of the honeycomb. This feature further contributes to the lowering of the thermal expansion of the honeycomb body. However, the attainment of the proper microstructure required for these low expansions in conventional cordierite ceramic bodies is highly dependent on the chemistry, crystalline structural state, and particle sizes of the individual raw material components.
It would be highly desirable and an advancement in the art to have a method of making low-expansion cordierite bodies in which the low thermal expansion does not rely on preferred orientation of the cordierite crystallites and in which the thermal expansion coefficient is less sensitive to the chemistry, mineralogy, and particle size of the raw materials.
This invention provides such a method by utilizing certain glass frit powders.